AbstractResistance responses of resynthesizedBrassica napuslines to infection withPlasmodiophora brassicaewere investigated. Lines that were derived from interspecific crosses between clubroot‐resistantB. rapaand resistantB. oleraceaexhibited very broad and effective resistance in both greenhouse and field tests. When clubroot resistance was introduced into resynthesized lines from theB. oleraceaparent only, the plants were mainly susceptible. Interspecific hybrids from the most resistant parental genotypes, i.e.B. campestrisECD‐04 and theB. oleraceacultivars ECD‐15 or ‘Bohmerwaldkohf’, were used to initiate aB. napusresistance‐breeding programme. These artificial rapeseed lines were resistant to isolates that were virulent on allB. napusdifferential lines and/or parental lines. Preliminary segregation analysis suggests that their resistance is due to at least two dominant and unlinked genes. In some cases progenies from selfed resynthesized plants exhibited resistance reactions that differed from those of the parental hybrid plant; this may have been the result of cytological